Modern wireless transmitters (e.g. for cellular communication, Bluetooth communication or Wi-Fi communication) are dominated by two architectures: Cartesian (I/Q) transmitters and polar transmitters.
A Cartesian transmitter uses a Radio Frequency Digital-to-Analog Converter (RF-DAC) to generate a modulated radio frequency (RF) signal directly from a complex valued symbol having an in-phase component and a quadrature component. Two Local Oscillator (LO) signals of a same frequency, shifted by 90°, are used to clock the RF-DAC. The LO signals represent the in-phase and quadrature axes (vectors) of the constellation diagram. Cartesian architecture may handle modulation schemes with high bandwidth, but has a lower efficiency than polar architecture.
In polar architecture, a symbol is expressed by phase and amplitude information. Conventional polar transmitters may use a Phase-Locked-Loop (PLL) for phase modulation of a LO signal. More sophisticated polar transmitters may use a Digital-to-Time Converter (DTC) to apply phase modulation and/or frequency shifts on a constant LO signal. The modulated output of the DTC may be used to clock a RF-DAC. The RF-DAC may apply amplitude modulation and adjust an output power of the RF signal. One advantage of polar architecture including a DTC may be a high efficiency of the output stage and that only a single PLL may provide the LO signal for multiple transmitters. However, handling RF signals with a wide bandwidth is problematic with polar architecture.
Hence, there may be a desire for an improved transmitter architecture.